This allows you to look at the current DPM state via
debugfs.

Due to the way the hardware works on these asics, there's
no way to look up exactly what power state we are in, so
we make the best guess we can based on the current sclk.

v2: Anthoine's version
v3: fix ref div
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

This adds dpm support for rs780/rs880 asics.  This includes:
- clockgating
- dynamic engine clock scaling
- dynamic voltage scaling

set radeon.dpm=1 to enable it.
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>